1. Field of Use
This invention relates generally to an improved seating seal means for a disc-type stop valve.
2. Description of the Prior Art
Disc-type stop valves are used in various systems to control the flow of liquids and gases and are particularly well suited to control the flow of refrigerants, whether in the gaseous or liquid states, which are circulated under extremely high pressure in refrigeration systems. Such valves typically range in size, for example, from 1" to 8" when measured with reference to the diameter of the valve's inlet/outlet ports.
A typical disc-type stop valve generally comprises a valve housing having an inlet port, an outlet port and an annular valve seat within the housing between the two ports. An externally threaded rotatable valve stem extends through an internally threaded, sealed, valve-stem opening in the housing and is provided at its lower end with a circular valve disc which is axially movable into and out of engagement with the annular valve seat as the valve stem is manually (or otherwise) rotated between closed and open positions, respectively.
The prior art teaches various forms of seating seal means which aim to improve the seal between the valve disc and the annular valve seat to prevent undesirable leakage through the valve when the valve is closed. In one known prior art type of disc-type stop valve used in high pressure refrigeration systems, the valve disc which is located at the lower end of the rotatable valve stem takes the form of a solid cylindrical metal member. The valve disc is connected to the valve stem in such a manner that there is some "play" or relative movement possible between them so that the valve disc can adjustably position itself on the valve seat. The valve disc has an annular groove formed around the outer periphery of its lower surface and an annular seal ring made of plastic, such as TEFLON for example, is disposed in the groove for engaging the valve seat. The plastic seal ring is held in place on the valve disc by a smaller-diameter circular metal retainer plate which is attached to the lower surface of the valve disc and bears against the underside of the seal ring. The retainer plate is secured to the valve disc by a plurality of bolts which extend through holes in the retainer plate and screw into threaded bolt holes in the valve disc. When the valve is closed, the lower corner edge of the plastic seal ring bears against the annular conically-shaped metal valve seat surface in the valve body.
Since the plastic seal ring is slightly resiliently compressible and is also highly wear-resistant, it is able to deform slightly so as to evenly and tightly engage the valve seat surface to provide an even and tight seal when the valve is tightly closed. Upon opening the valve, the resilient plastic seal ring is able to resume its normal shape. The plastic seal ring also has a very low coefficient of friction and resists wear and damage resulting from repeated closures wherein it is tightly pressed against the metal valve seat.
Because of the high fluid pressure conditions which exist at the underside of the valve disc when the valve is closed, there is a possibility of gas or liquid leakage along the following path: through a first space between the rear side of the retainer plate and the front side of the seal ring, through a second space between the inner edge of the sealing ring and the side edge of the annular groove in the valve disc, and through a third space between the rear side of the seal ring and the bottom of the annular groove in the valve disc. Furthermore, when the valve is cracked open slightly, the restricted, high velocity flow of fluid from the high pressure to the low pressure side of the valve through the small opening or space between the valve seat and the seal ring creates a condition whereby fluid can leak through the aforedescribed path. Furthermore, the result of such leakage is that high pressure fluid in the aforesaid second space causes the resilient plastic seal ring to expand or be urged laterally or circumferentially outward relative to the groove due to fluid pressure in the aforementioned second space. Over time, such a phenomenon has the effect of permanently deforming and loosening the plastic seal ring and increasing the possibility of undesirable fluid leakage through the aforesaid flow path when the valve is fully closed.
Heretofore, efforts to prevent fluid leakage and the phenomena described hereinbefore entailed tightening the bolts as much as possible so that the plastic seal ring is tightly compressed in the groove in the valve disc by the metal retainer plate which traps the seal ring in the groove. However, because the TEFLON seal ring required the application of a great deal of force to compress it for even a small amount, and because the bolts involved were necessarily relatively small and few in number, application to the bolts of the high torque required to sufficiently compress the seal ring, often resulted in shearing of the bolts or thread damage thereby substantially increasing the time, labor and cost of manufacturing such a valve.